The present invention relates to a dense silicon nitride material having a novel composition and, in particular, relates to an improved silicon nitride material incorporating strontium carbonate, as a green state material, and yttrium oxide which are used as sintering aids to produce the dense silicon nitride material having high strength over a wide range of temperatures.
Sintered silicon nitride materials are well-known in the art. However, silicon nitride materials are usually limited in that the materials do not exhibit high strength and long stress rupture life when utilized in a high temperature (greater than 1000.degree. C.) environment. It is known that sintering aids have been utilized in order to increase the density of the sintered material which in turn increases the mechanical strength. It is also known that the incorporation of yttrium oxide (Y.sub.2 O.sub.3) is and remains one of the most utilized sintering aids to increase the properties of sintered silicon nitride materials. Furthermore, it is known to use strontium oxide (SrO) as a sintering aid with silicon nitrides, however, strontium oxide is unstable and reacts with the atmosphere and therefore degrades prior to the final formation of the silicon nitride material. In addition, strontium oxide is much more expensive than strontium carbonate which is stable.